An Impedance Model for Lithium-Ion Capacitors Incorporating Voltage, Temperature, and Aging Effects

Abstract

A lithium-ion capacitor (LIC) is a hybrid energy storage device combining both the capacitive behavior of supercapacitors (SCs) and the battery-like response of lithium-ion batteries. This article presents an equivalent circuit model (ECM) for the impedance capturing the dual electrochemical behavior of LICs across different operating voltages, extending conventional models of SCs to include the non-ideal capacitive effects of the lithiated negative electrode included in the hybrid technology. The parameters of the ECM were found to be highly dependent on voltage and temperature values, which were directly correlated with the electrochemical phenomena inside the cells. Impedance data extracted during accelerated aging tests were also used to analyze the effects of aging on the parameters of the ECM. A generalized model that can incorporate an Arrhenius-based degradation factor to account for the combined effects of temperature and aging was developed. The model was validated by comparing experimental data to estimated ones, with root mean square error values below 5%, demonstrating its suitability for accurately predicting LICs behavior under varying voltages, temperatures, and life cycles.